Although prosthetic knee joints for transfemoral prostheses have traditionally been energetically passive devices, powered, semi-autonomous knee joints have recently started to emerge in the research community and on the commercial market. Typically, passive knee prostheses can only react to mechanical energy imparted by the amputee, while powered knee prostheses have the ability to act independently of mechanical energy from the user. As such, the nature of the user communication with the powered prosthesis and control of the powered prosthesis is substantially different from the control of a traditional, energetically passive prosthesis.
Various methods have been proposed for the control of powered knee prostheses. These approaches typically utilize instrumentation on at least one of the prosthesis or a sound leg. Such instrumentation can include inertial measurement sensors (accelerometers and/or gyroscopes) at the foot, shank or thigh of the prosthesis and/or sound side. Additionally, joint angular position, velocity and torque sensors for ankle, knee and hip joints of the prosthesis and/or sound side can also be used as instrumentation for prosthesis control. Further, ground force detecting load cells or load switches can also be used to detect events such as heel strike or toe-off. This instrumentation is used to form knee joint angle trajectories or impedances for the powered knee prosthesis during activities involving the prosthesis. For example, while standing, walking, or transitioning between sitting and standing.
In general, activities such as standing, walking, or transitioning between sitting and standing all involve physical input and/or energy exchange between the residual limb and prosthesis. Therefore, most conventional methods rely on some form of physical input from the user for communication with the powered knee prosthesis. That is, although the user need not provide the energy for movement, as is the case with traditional dissipative knee prostheses, the user must still provide some physical input that can be measured by instrumentation on the prosthesis and/or sound leg. Such physical inputs include measuring weight bearing on the prosthesis, torque and/or acceleration from the affected-side hip joint, movement of the sound-side leg, to name a few.
An important class of movement, however, which does not involve any significant physical input from the user, is the task of non-weight-bearing or volitional control of knee movement while sitting or standing. That is, people regularly shift their body while sitting, which involves significant movement of the knee joints. Such movement has both physiological and practical purposes. Regarding the former, weight shifting during sitting is known to play an important role in ensuring healthy circulation of blood in weight-bearing tissues during sitting. Regarding the latter, sitting in confined areas, such as in automobiles, airplanes, theatres, and classrooms, often requires shifting of body position (particularly of the knee joints) in order to accommodate a particular ergonomic space and/or the movement of other individuals into or out of that space. Such movement is referred to herein as volitional control of the knee joint during non-weight-bearing activity. Note that such volitional control is also useful in non-weight-bearing standing, such as when flexing the knee to look at the bottom of a shoe, or when placing the foot on an elevated surface (such as a chair) to tie or untie, or don or doff a shoe. In the case of a traditional, energetically passive prosthesis, an amputee typically achieves “volitional” control functionality by manipulating the prosthetic knee leg with his or her hands.